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In a piston engine if the ratio of air to fuel is approximately 9:1 the mixture is:
  • A
    too weak to support combustion.
  • B
    weak.
  • C
    chemically correct.
  • D
    rich.

Refer to figure.

This question is simply asked to see if you understand how the mixture ratio works. 15:1 mixture ratio means that for every 1 gram of fuel, 15 grams of air are required. Therefore, a rich mixture means that there’s less mass of air supplied for one gram of fuel than for a leaner mixture.
A ratio of 9:1 means that for every gram of fuel, 9 grams of air are required. By comparing it to the chemically correct ratio, you can deduce that a 9:1 ratio represents a rich mixture.

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